slab: document SLAB_DESTROY_BY_RCU
Explain this SLAB_DESTROY_BY_RCU thing... [hugh@veritas.com: add a pointer to comment in mm/slab.c] Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Jens Axboe <jens.axboe@oracle.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Christoph Lameter <cl@linux-foundation.org> Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
This commit is contained in:
parent
02f5621042
commit
d7de4c1dc3
|
@ -23,6 +23,34 @@
|
|||
#define SLAB_CACHE_DMA 0x00004000UL /* Use GFP_DMA memory */
|
||||
#define SLAB_STORE_USER 0x00010000UL /* DEBUG: Store the last owner for bug hunting */
|
||||
#define SLAB_PANIC 0x00040000UL /* Panic if kmem_cache_create() fails */
|
||||
/*
|
||||
* SLAB_DESTROY_BY_RCU - **WARNING** READ THIS!
|
||||
*
|
||||
* This delays freeing the SLAB page by a grace period, it does _NOT_
|
||||
* delay object freeing. This means that if you do kmem_cache_free()
|
||||
* that memory location is free to be reused at any time. Thus it may
|
||||
* be possible to see another object there in the same RCU grace period.
|
||||
*
|
||||
* This feature only ensures the memory location backing the object
|
||||
* stays valid, the trick to using this is relying on an independent
|
||||
* object validation pass. Something like:
|
||||
*
|
||||
* rcu_read_lock()
|
||||
* again:
|
||||
* obj = lockless_lookup(key);
|
||||
* if (obj) {
|
||||
* if (!try_get_ref(obj)) // might fail for free objects
|
||||
* goto again;
|
||||
*
|
||||
* if (obj->key != key) { // not the object we expected
|
||||
* put_ref(obj);
|
||||
* goto again;
|
||||
* }
|
||||
* }
|
||||
* rcu_read_unlock();
|
||||
*
|
||||
* See also the comment on struct slab_rcu in mm/slab.c.
|
||||
*/
|
||||
#define SLAB_DESTROY_BY_RCU 0x00080000UL /* Defer freeing slabs to RCU */
|
||||
#define SLAB_MEM_SPREAD 0x00100000UL /* Spread some memory over cpuset */
|
||||
#define SLAB_TRACE 0x00200000UL /* Trace allocations and frees */
|
||||
|
|
Loading…
Reference in a new issue